Veins are thin-walled and contain one-way valves that control blood flow. Normally, the valves open to allow blood to flow into the deeper veins and close to prevent back-flow into the superficial veins. When valves are malfunctioning or only partially functioning, however, they no longer prevent the back-flow of blood into the superficial veins. As a result, venous pressure builds at the site of the faulty valves. Because the veins are thin walled and not able to withstand the increased pressure, they become what are known as varicose veins which are veins that are dilated, tortuous or engorged.
In particular, varicose veins of the lower extremities is one of the most common medical conditions of the adult population. It is estimated that varicose veins affect approximately 25% of adult females and 10% of males. Symptoms include discomfort, aching of the legs, itching, cosmetic deformities, and swelling. If left untreated, varicose veins may cause medical complications such as bleeding, phlebitis, ulcerations, thrombi and lipderatosclerosis.
Endovascular thermal therapy is a relatively new treatment technique for venous reflux diseases such as varicose veins. With this technique, the thermal energy is delivered by a flexible optical fiber or radiofrequency electrode that is percutaneously inserted into the diseased vein prior to energy delivery. For laser delivery, a treatment sheath is typically inserted into the vein at a distal location and advanced to within a few centimeters of the source of reflux. Once the treatment sheath is properly positioned, a flexible optical fiber is inserted into the lumen of the treatment sheath and advanced until the fiber tip is near the treatment sheath tip but still protected within the sheath lumen.
Prior to laser activation, the treatment sheath is withdrawn approximately 1-4 centimeters to expose the distal tip of the optical fiber. After the fiber tip has been exposed a selected distance beyond the treatment sheath tip, a laser generator is activated causing laser energy to be emitted from the bare flat tip of the fiber into the vessel. The emitted energy heats the blood causing hot bubbles of gas to be created. The gas bubbles transfer thermal energy to the vein wall, causing cell necrosis, thrombosis and eventual vein collapse. With the laser generator turned on, both the optical fiber and treatment sheath are slowly withdrawn as a single unit until the entire diseased segment of the vessel has been treated.
A typical laser system uses a 600-micron optical fiber covered with a polymer jacket and cladding layer. The fiber core extends through the fiber terminating in an energy emitting face.
With some prior art treatment methods, contact between the energy-emitting face of the fiber optic tip and the inner wall of the varicose vein is recommended to ensure complete collapse of the diseased vessel. For example, U.S. Pat. No. 6,398,777, issued to Navarro et al, teaches either the means of applying pressure over the laser tip or emptying the vessel of blood to ensure that there is contact between the vessel wall and the fiber tip. One problem with direct contact between the laser fiber tip and the inner wall of the vessel is that it can result in vessel perforation and extravasation of blood into the perivascular tissue. This problem is documented in numerous scientific articles including “Endovenous Treatment of the Greater Saphenous Vein with a 940-nm Diode Laser: Thrombotic Occlusion After Endoluminal Thermal Damage By Laser-Generated Steam Bubble” by T. M. Proebstle, MD, in Journal of Vascular Surgery, Vol. 35, pp. 729-736 (April, 2002), and “Thermal Damage of the Inner Vein Wall During Endovenous Laser Treatment: Key Role of Energy Absorption by Intravascular Blood” by T. M. Proebstle, MD, in Dermatol Surg, Vol. 28, pp. 596-600 (2002), both of which are incorporated herein by reference. When the fiber contacts the vessel wall during treatment, intense direct laser energy is delivered to the vessel wall rather than indirect thermal energy from the gas bubbles from heating of the blood. Laser energy in direct contact with the vessel wall causes the vein to perforate at the contact point and surrounding area. Blood escapes through these perforations into the perivascular tissue, resulting in post-treatment bruising and associated discomfort.
Another problem created by the prior art methods involving contact between the fiber tip and vessel wall is that inadequate energy is delivered to the non-contact segments of the diseased vein. Inadequately heated vein tissue may not occlude, necrose or collapse, resulting in incomplete treatment. With the fiber tip in contact with the vessel wall rather than the bloodstream, hot gas bubbles are not created. The bubble is the mechanism by which the 360 degree circumference of the vessel wall is damaged. Without the bubbles, it is possible for some vein tissue to be under heated or not heated at all, resulting in incomplete treatment and possible recanalization of the vessel.
A related problem with endovascular laser treatment of varicose veins using a conventional fiber device is fiber tip damage during laser energy emission caused by localized heat build up at the working end of the fiber, which may lead to thermal runaway. Thermal runaway occurs when temperature at the fiber tip reaches a threshold where the core and/or cladding begin to absorb the laser radiation. As the fiber begins to absorb the laser energy it heats more rapidly, quickly spiraling to the point at which the emitting face begins to burn back like a fuse. One cause of the heat build up is the high power density at the emitting face of the fiber. A conventional fiber includes a cladding layer immediately surrounding the fiber core. Laser energy emitted from the distal end of the device may create thermal spikes with temperatures sufficiently high to cause the cladding layer to burn back. Once the cladding layer is no longer present, laser energy will travel through the side wall of the fiber, causing additional energy loss and localized heating. The fiber weakens under the high temperatures and may break.
In a related problem with conventional endovenous laser treatment methods, numerous procedural steps and accessory components are required to correctly position the optical fiber at the treatment site prior to the application of laser energy. The procedure is time-consuming and expensive partially due to the costs of the accessory components, which includes a treatment sheath designed to provide a pathway for the fiber to be advanced through the vessel to the source of reflux. The introduction of multiple components including the treatment sheath requires a large access site puncture which may result in patient complications including bruising, prolonged bleeding, scarring, and infection.
Therefore, it would be desirable to provide an endovascular treatment device and method that protects the emitting face of the optical fiber from direct contact with the inner wall of vessel during the emission of laser energy to ensure consistent thermal heating across the entire vessel circumference thus avoiding vessel perforation and/or incomplete vessel collapse.
It is also desirable to provide an endovascular treatment device and method which decreases peak temperatures at the working end of the fiber during the emission of laser energy thus avoiding the possibility of fiber damage and/or breakage due to heat stress caused by thermal runaway.
It is yet another purpose to provide an endovascular treatment device and method which reduces the number of accessory components and procedural steps required to successfully treat a blood vessel.
Various other purposes and embodiments of the present invention will become apparent to those skilled in the art as more detailed description is set forth below. Without limiting the scope of the invention, a brief summary of some of the claimed embodiments of the invention is set forth below. Additional details of the summarized embodiments of the invention and/or additional embodiments of the invention may be found in the Detailed Description of the Invention.